Manufacture of abrasive articles



July 18, 1933. R. c. BENNER El AL 1,918,242

MANUFACTURE OF ABRASIVE ARTICLES Filed Oct. 23. 1929 INVENTORS RAYMOND a. BENNER PRESCOTT H.WAL R GNARLES E.. W00 ELL 5M, h M, W

A TTORNEYJ' Patented July 18, 1933 UNITED STATES PATENT OFFICE RAYMOND C. BENNER, PRESCOTT H. WALKER, AND CHARLES E. WOODDELL, OF N IAGARA FALLS, NEW YORK, ASSIGNORS TO THE CARBORUNDUM COMPANY, OF NIAGARA FALLS, NEW YORK, A CORPORATION OF PENNSYLVANIA MANUFACTURE OF ABRASI'VE ARTICLES Application filed October 23, 1929. Serial No. 401,963.

This invention relates to the manufacture of bonded abrasive articles and particularly that class of articles involving the use of a binder of ceramic or similar nature.

In the usual method of manufacturing bonded abrasive articles, the abrasive grains have been mixed with a clay or a combination of clays and the mixture tempered with water and a small percentage of temporary binder and then formed into an article by either pressure or tamping or a combination of the two, with subsequent drying and curing at elevated temperatures. A large number of clays or mixtures of clays have been use in the abrasive art, but in all cases the curing operation has comprised vitrification, or in other words, liquefaction of the binding material, and subsequent reaction between the ingredients to form a more or less homogeneous mixture.

The usual curing operation has extended over periods of time ranging from two to seven days, during which the binding material has been a liquid of low viscosity and of little value in supporting the article undergoing vitrification. One of the difliculties arising from this lon period of fluidity of the bond has been t e great tendency for abrasive articles to undergo slumping during the curing operation. As a result of this slumpin action, abrasive articles have been limited in size, because slumping naturally is a function of not only the fluidity of the bond, but of the size of the article, the time required for maturing and the readiness with which the bond wets the grain. The net result of this in the prior art has been the restriction of abrasive articles to the smaller sizes, e. g. 30 or less inches in diameter and 8 or less inches in thickness, with the consequence that manufactured abrasive articles have not completely replaced the natural abrasive article which can be quarried in large pieces.

The accompanying drawing illustrates a method of carrying out the final step of firing a large abrasive article when our invention is practiced, and in the drawing:

Figure 1 represents a transverse vertical section through the abrasive article and the materials for supporting it in the kiln; and

Figure 2 is a horizontal section through the assembly shown in Fig. 1.

We have found that one of the principal difiiculties in the manufacture of lar abrasive articles resides in the fact that t e usual practice involves the use of such materials as clay or mixtures of clays and fluxing materials which require a considerable time at elevated temperatures to cause the heterogeneous ingredients to unite and roduce uniformity in the resulting wheel. uring the vitrification period these materials are liquids of low viscosity and are of little value in supporting the abrasive grain forming the article. As a consequence of this liquid state of the binding material, articles of large size frequently slump so badly in the vitrification operation that they cannot be used for the purpose intended. Slumpin is not so prevalent in the smaller articles cause of the fact that they are of lesser weight.

Slumping is a function not only of the size of the article and the liquid state of the binder, but also of the length of time during which the article is maintained at a temperature suflicient to liquefy the bond and cause it to wet the grain. If the ordinary vitrification process could be shortened to such an extent that the maximum temperature was maintained for only a few minutes or less than an hour, it might be possible to cure large articles without slumping, but the nature of the binding materials used in the past has required the maintenance of the maximum temperature for a period of as long as seven days in order to permit the ingredients to react and form the ultimate product.

We have found that large articles may be made by using a binder which has been carried to such a state of vitrification that a glass is formed and no further reaction will take place at the temperature of the burning operation in the manufacture of the abrasive article. The use of this glass material thus enables us to curethe articles by bringing them to the melting point of the bond and maintaining that temperature only for the period of time required to assure uniformity of temperature throughout the article.

However, the use of the glass binder as disclosed above introduces another difficulty, namely, the provision of satisfactory strength in the green or uncured article. Articles made in accordance with the prior practice have included a considerable quantity of plastic clay which imparts to the article sufficient plasticity to enable one to handle the formed article with little difficulty, but powdered glass is not plastic and cannot therefore impart plasticity to the abrasive mix and consequently the articles are very fragile in the uncured state. In the prior art such materials as dextrin, linseed-oil, residues from the sulphite pulp cooking process and other organic materials have been used to increase the plasticity of mixes which require greater strength than that produced by the clay contained therein. Other ceramic processes have involved the use of small percentages of sodium silicate. We have found, however, that the organic materials mentioned are not satisfactory for use in large articles because of the difficulty of burning the carbonized residues out of thick sections, and that the usual small percentages of sodium silicate are insufliicent for the production of a satisfactorily strong article. Whereas sodium silicate has been used in the prior art in an amount usually less than 2 to 3 per cent of the total weight of the mixture, we have found it possible to use as much as 5 or 6 per cent of sodium silicate in our mixtures, and that by using sodium silicate to the extent of 5 or 6 per cent we can produce an article which is of sufficient strength to be transported and loaded into the kiln after it has received a preliminary baking treatment, as for example, to the temperature of approximately 200 degrees centigrade.

The use of such large percentages of sodium silicate has not been feasible in the prior art because of its fluxing action on the clay-like portion of the mixture, but by the use of a mixture comprising inert abrasive grain and finely divided particles of inert glass, we can use a higher percentage of sodium silicate without causing the articles to bloat during the curing operation.

A modification of the above consists in adding to the temporary binder materials which serve to eliminate or at least to reduce the tendency of the sodium silicate to bloat and puff up during the baking operation. Moreover, we have found that the incorporation of these materials, particularly with acid glasses, has the advantage of providing means for controlling the characteristics of the ultimate binder and affords means for offsetting the effect of the alkali contained in the sodium silicate on the coefficient of expansion of the principal binder. Thus, by incor orating with the sodium silicate other materials, we are enabled not only to eliminate the difficulty arising from the incorporation of sodium silicate, but at the same time we accomplish other desirable results.

The combination of materials including the sodium silicate and the modifying materials is readily assimilated by the glass and the resulting binder after the final heat treatment is more homogeneous and may be controlled in respect to its temperature coefficient of expansion more closely than is possible where materials which require long periods of time for interaction of the various ingredients comprising the binding materials are used. Moreover, the ra id assimilation of the sodium silicate an modifying materials by the glass reduces the time required for maturing the bond.

In the typical examples given below we disclose the use of such materials as zinc oxide and flint as the modifying agents for the temporary binder, and we have found that the sodium silicate when combined with zinc oxide and flint and baked provides a temporary binder which is stronger than sodium silicate itself and which also is more waterproof. We have found also that zinc oxide and flint afford the advantage that they may be used to offset the effect of the addition of the alkali contained in the sodium silicate, it being the object of this invention to provide a bond which does not become too fluid at the elevated temperature and as is well known in the art the addition of sodium silicate is apt to lower the viscosity of the molten glass. Thus, by adding to the sodium silicate materials which counteract the fluxing action of the silicate we can form large articles with considerable strength in the green state and at the same time avoid the inherent difficulty attending the use of sodium silicate in combination with glass material.

We have found that in addition to its function as an intermediate binder, the mixture of silicate of soda, zinc oxide and flint serves another useful purpose in altering the fragility of the glass binder. Glasses of the type we prefer to use are usually very tough and produce an abrasive article which likewise is tough, but by adding silicate of soda, zinc oxide and flint the toughness of the bond is reduced and a more fragile bond results. Increased amounts of the mixture of silicate of soda, zinc oxide and flint cause increased fragility and thereby enable us to control the character of the resulting bonded abrasive.

Zinc oxide has the specific advantage of offsetting the effect of sodium silicate on the coefficient of expansion of the principal binder used in that the higher the zinc proportion, within limits, the greater the thermal endurance of the resultant article, this greater thermal endurance resulting probably from the lowered coefficient of expansion and great product of the Aluminous abrasive particles 7 85 7 93 7 Powdered glass 20 7g 9. 2% 4.1%

Sodium silicate l. 6.9% 4. 0% 2. 0'7

Powdered mm 1.7% 1.0% .57;

Zinc oxide 1.4% .8% .4%

The quantity of zinc oxide and the quantity of flint added to the mix are both dependent upon the amount of sodium silicate used, and in general are combined in the proportion of 69 parts silicate, 13.7 parts zinc oxide and 17.3 parts flint, all by weight.

The bond compositions disclosed above may be varied both as to amounts and ingredients to secure certain desired results. For example, the bond content may be adjusted to secure harder or softer articles. The composition of the sodium silicate may be varied to include higher or lower ratios of silicate to soda, as may be desired, or a part of all of the zinc oxide may be replaced by boric anhydride. When boric anyhdride is added tot the mix a borosilicate glass is formed in $1 u.

We have found that glasses containing a high ratio of acid oxides to basic oxides have coeflicients of expansion which are lower than that of the abrasive grain and that these glasses remain viscous at the curin temperature employed. However, while these glasses are viscous at the temperatures employed in curing, they readily wet the abrasive particles at these temperatures and form a bond which adheres well to the grain.

Glasses of simple composition have been found very satisfactory for bonding the abrasive grains into unitary articles. For example, glasses composed principally of S10 B O A1 0 and Na O possess the requisite viscosity and grain wetting ability, particularly if themolecular ratio of SiO to Na O is greater than thirteen (13) to one and the molecular ratio of acidic oxides to basic oxides is not less than fifteen (15) to one. Moreover, glasses of this nature have coefficients of expansion less than .000004 per C. and have a softening temperature greater than 800 C. and less than 900 C. as determined by noting the temperature in degrees centigrade at which a thread of the glass 1 mm. thick and 23 cm. in length suspended vertically and heated through the upper 9 cm. elongates of its own weight at the rate of 1 mm. per minute.

A glass containing SiO B 0 A1 0 and ZrO but no alkali or alkaline earth has a very low coeflicient of expansion (.000007) and may be used when a bond of low expansivity is required. Such a glass may contain from SOto 90 percent SiO and from 9 to 17 per- -cent B 0, with the A1 0, and ZrO contents approximately equal and less cent.

The type of glass which we prefer to use ordinarily would be rejected on account of its high fusion temperature and the consequent requirement for a high maturing temperature in curing the abrasive articles. By way of example, a glass containing approximately 81% SiO 5 Na O 1 A1 0, 100% can be poured only with difliculty at a temperature of 1500 C., and, as stated above, has a hardness of more than 800 C., whereas the usual commercial glasses have a hardness of less than 600 C. and are quite fluid at temperatures below 1300 C.

In carrying out our invention we mix together the dry ingredients comprising the abrasive grains and the bonding ingredients, and then add to the mixture an adhesive substance such as sodium silicate solution, and then, after the materials have been thoroughly mixed, we form the article in a. mold by any suitable method, such as tamping or tamping and pressing and bake it at approximately 200 C.

The baking operation by which we prefer to cause the temporary binder to assume a set or hardened condition must be controlled carefully in order to provide an article which is sound and in order to bring out the maximum stren h and water resistance of the temporary inder. As an example of the method We employ in causing the temporary binder to set we proceed as follows:

The mold completely enclosing the formed article is placed in an oven which is already at a temperature of 135 C. and the temperature of the oven is then raised gradually until the temperature of 200 is reached. In general, the rate of heating the oven from the original temperature to that of the maximum just stated is approximately 15 per hour. When the maximum temperature has been reached the article is held at that temperature for four to eight hours and then permitted to cool at the rate of approximately 25 per hour.

The baking operation disclosed above enables us to make large articles conveniently and safely because the set of the temporary binder can be accomplished without removing the article from the metal mold. This step of making the article in the mold in which it was formed has the further advantage that it reduces the tendency of the temporary binder to release its water too rapidly and thus cause a shattering of the bond. In fact, it is believed that the setting of the temporary binder takes place in the article than 1.5 per enclosed by the mold without the removal of any substantial portion of the water contained in the binder.

In some cases, where the amount of sodium silicate is very low and the articles are of small size, it is not essential that the article be baked in its mold. However, the baking schedule employed when the wheels are first removed from the molds is essentially the same as that of the method described above except that the article is not placed in the oven at an elevated temperature directly after the moldin operation but is set aside for approximate y twelve hours to permit evaporation of a portion of the water con tained in the silicate. When the articles are in the drying process it is desirable to turn them once or twice during the twelve hour drying period in order to secure uniform conditions throughout the structure.

After the article has been heat-treated or baked, as this operation is usually designated, at a temperature of approximately 200 C., We remove it from the mold and set it in a kiln for further heat treatment. The operation of setting the article in the kiln is carried out in the usual manner and comprises laying it on a level ceramic plate upon which is a thin layer of approximately 1 to 2 inches of granular refractory material, and then gently rotating the article back and forth to insure perfect seating.

In some cases, as shown in the drawing, we may place an iron band 2 of large diameter around the outside of the wheel and another iron band 3 of smaller diameter than the arbor hole of the wheel in the center of the arbor. The intervening spaces between the wheel and the bands are then filled with granular refractory material 4 such as sand or crushed quartz. The band placed in the hole of the wheel should be capable of becoming of lesser diameter as the wheel contracts upon cooling and compresses the granular material in the space between the wheel and the band. By placing these bands around the wheel and within the arbor hole and filling the intervening spaces with granular material we provide the means whereby slumping is reduced or eliminated. These bands must, however, not be so rigid and unyielding that they resist the natural expansion of the article upon heating and the natural contraction of the article upon cooling. The bands are supported on a slab or ceramic plate 5, which plate also retains the sand or other refractory in place within the rings.

While we have shown and described a present preferred method of carrying out our invention, it will be understood that the invention is not confined to the particular ingredients herein specifically disclosed, and that various modifications may be made in the practice of the invention under the scope of the following claims.

We claim:

1. An abrasive article comprising abrasive particles bonded with a fused zinc borosilicate glass bond.

2. An abrasive article comprising abrasive grains bonded with a zinc borosilicate bond, the bond being fused to form a glass.

3. An abrasive article comprising aluminous abrasive grains bonded with a fused zinc borosilicate glass bond.

4. An abrasive article comprising abrasive grains and a bond comprising the fusion product of alkaline silicate, zinc oxide and borosilicate glass.

5. An abrasive article comprising abrasive particles and a bond, said bond being the fusion product of zinc oxide, alkaline silicate, flint and borosilicate glass.

6. An abrasive mix for the production of abrasive articles comprising a rasive particles, zinc oxide, alkaline silicate in a wet form, and powdered borosilicate glass.

7. An abrasive mix for the production of abrasive articles comprising abrasive grains, zinc oxide, flint and alkaline silicate in a wet form and powdered borosilicate glass.

8. An abrasive mix for the production of abrasive articles comprising abrasive articles, zinc oxide, alkaline silicate in a wet form, and powdered borosilicate glass, the alkaline silicate constituting at least 5% by weight of the mix.

9. An abrasive mix for use in the production of abrasive articles, comprising aluminous abrasive grains ranging between approximately 70% and 95% by weight of the total mix, powdered borosilicate glass ranging between 20% and 4.1%, sodium silicate ranging between 6.9% and 2% powdered flint ranging between 1.7% and .5% and zinc oxide ranging between 1.4% and .4%.

10. An abrasive article comprising aluminous abrasive grains and a bond comprismg a fusion product of powdered borosilicate glass, a water-soluble alkaline silicate, and a metallic oxide capable of resisting the bloating tendenc of the sodium silicate.

11. An a rasive article comprising aluminous abrasive grains and a bond comprising the fusion product of powderedborosilicate glass, a water-soluble alkaline silicate, flint, and a metallic oxide capable of resisting the bloating tendency of the sodium silicate.

12. An abrasive article comprising abrasive grains and the fusion product of a waterinsoluble glass containing at least of acidic oxides, and alkaline silicate glass and zinc oxide.

13. In the manufacture of abrasive articles, the steps which comprise mixing abrasive grains with powdered borosilicate glass, a solution of an alkaline silicate, and a substance for counteracting and offsetting the substance for offsetting the fluxing and bloating tendency of the alkaline silicate.

14. In the manufacture of abrasive articles, the steps which comprise mixing abrasive grains with powdered borosilicate glass, a solution of an alkaline silicate, and a substance for counteracting and offsetting the bloating and fluxing tendency of the alkaline silicate, forming an article from said mix within a mold, baking the article in a mold to give a primary setting to the alkaline silicate, removing the article from the mold, and thereafter firing it to form a homogeneous bond through the fusion of the borosilicate glass, the alkaline silicate and the addition substance for offsetting the fluxing and bloating tendenc of the alkaline silicate, the fusing. being e ected at a temperature at which the fusion product is sufficiently viscous to wet the abrasive grains but below the temperature at which it will flow through or out of the molded form.

15 In the manufacture of abrasive articles, the steps which comprise forming an abrasive mix from aluminous abrasive grains, finely divided borosilicate glass, and wetting the same with an alkaline silicate, and further incorporating a metallic oxideand flint into the mix to eliminate the pufling and bloating of the article formed from the mix, forming an article from the mix in a mold, baking the article in the mold to congeal the alkaline silicate and impart a preliminary set to the article, and thereafter firing the article to fuse the borosilicate glass, the alkaline silicate and the metallic oxide and flint into a homogeneous binder.

16. The steps in the process of manufacturing very large artificially bonded abrasive wheels which comprise mixing aluminous abrasive with powdered borosilicate glass and a much smaller proportion of sodium silicate, molding the wheel, heating the molded mixture to a temperature which forms a self-supporting article, placing refractory metal bands of greater coefficient of expansion than the abrasive wheel inside the arbor hole and around the periphery of the wheel, said bands being spaced from the wheel but concentric therewith, filling in the spaces between the wheel and the bands with sand, heating the assembly to a temperature sufiicient to make the borosilicate glass flow slowly over the abrasive grain in such a viscous condition that the shape of the wheel within its bedding is maintained, and cooling the assembly slowly under the pressure exerted by the metal bands.

RAYMOND C. BENNER. PRESCOTT H. WALKER. CHARLES E. WOODDELL.

EST AVAILABLE Copy bloating and fiuxing tendency of the alkaline silicate, forming an article from said mix within a mold, baking the article in a mold to give a primary setting to the alkaline silicate, removing the article from the mold, and thereafter firing it to form a homogeneous bond through the fusion of the borosilicate glass, the alkaline silicate and the addition substance for ofl'setting the fluxing and bloating tendency of the alkaline silicate.

14. In the manufacture of abrasive articles, the steps which comprise mixing abrasive grains with powdered borosilicate glass, a solution of an alkaline silicate, and a substance for counteracting and offsetting the bloating and fiuxing tendency of the alkaline silicate, formin an article from said mix within a mold, gaking the article in a mold to give a primary setting to the alkaline silicate, removing the article from the mold, and thereafter firing it to form a homogeneous bond through the fusion of the borosilicate glass, the alkaline silicate and the addition substance for offsetting the fiuxing and bloating tendenc of the alkaline silicate, the fusing being e ected at a temperature at which the fusion product is sufficiently viscous to wet the abrasive grains but below the temperature at which it will flow through or out of the molded form.

15 In the manufacture of abrasive articles, the steps which comprise forming an abrasive mix from aluminous abrasive grains, finely divided borosilicate glass, and wetting the same with an alkaline silicate, and further incorporating a metallic oxide and flint into the mix to eliminate the pufling and bloating of the article formed from the mix, forming an article from the mix in a mold, baking the article in the mold to congeal the alkaline silicate and impart a preliminary set to the article, and thereafter firing the article to fuse the borosilicate glass, the alkaline silicate and the metallic oxide and flint into a homogeneous binder.

16. The steps in the process of manufacturing very large artificially bonded abrasive wheels which comprise mixing aluminous abrasive with powdered borosilicate glass and a much smaller proportion of sodium silicate, molding the wheel, heating the molded mixture to a temperature which forms a self-supporting article, placing refractory metal bands of greater coelficient of expansion than the abrasive wheel inside the arbor hole and around the periphery of the wheel, said bands being spaced from the wheel but concentric therewith, filling in the spaces between the wheel and the bands with sand, heating the assembly to a temperature suflicient to make the borosilicate glass flow slowly over the abrasive grain in such a viscous condition that the shape of the wheel within its beddin is maintained, and cooling the assembly s owly under the pressure exerted by the metal bands.

RAYMOND C. BENNER. PRESCOTT H. WALKER. CHARLES E. WOODDELL.

CERTIFICATE OF CORRECTION.

\ Patent No. 1,918,242.

July 18, 1933.

RAYMOND c. BENNER, ET AL.

it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 4. line 95, claim 8, for articles" second occurrence read "particles"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 22nd day of August, A. D. 1933.

(Seal) M. J. Moore.

Acting Commissioner of Patents.

CERTIFICATE or CORRECTION.

Patent No. 1,918,242. July 18, I933.

RAYMOND C. BENNER, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 4. line 95, claim 8, for articles" second occurrence read "particles"; and that the said Letters Patent should be read with this correction therein that the same may eonfomt to the record of the case in the Patent Office.

Signed and sealed this 22nd day of August, A. D. I933.

M. J. Moore.

(Seal) Acting Commissioner of Patents. 

